Bell work question: 1/23/12

Please answer the bell work question of the day. Thank you!

1. Differentiate Intramembranous Ossification from Endochondral Ossification

Essentials of Anatomy and Physiology

Chapter 6:The Skeletal System

The AXIAL SKELETON

The Axial Skeleton can be divided into 3 parts:

the skull the vertebral column

the bony thorax

THE SKULL:

1) CRANIUM – enclose and protect the fragile brain tissue2) FACIAL BONES – present the eyes in an

anterior position and form the base of the facial muscles,which makes it possiblefor us topresent our feelings to the world.

•SUTURES – interlocking joint that joins all but one of the bones•The mandible and the lower jaw bone, is attached to the rest of the skull by a freely movable joint

Bones of the Skull and its important bone markings:

THE CRANIUM

•8 bones construct the cranium•With the exceptions of two paired bones : parietal and temporals ,all are single bones.•Sometimes the six ossicles of the middle ear are also considered part of the cranium but because the ossicles are part of the hearing apparatus, it is considered more part of the Special Sense.

The FRONTAL BONEanterior portion of the cranium; forms part of the forehead ,superior part of the orbit and the floor of the anterior cranial fossa Landmarks:1. Supraorbital foramen ( notch) –

opening above each orbit allowing blood vessels and nerves to pass.

2. Glabella- smooth area between the eyes

The PARIETAL BONE

posterolateral to the frontal bone; forming sides of the craniumLandmarks:1.Sagittal suture- midline articulation point of the two parietal bones2. Coronal Suture- point of articulation of parietals with the frontal bone

The TEMPORAL BONELocated below the parietal bones and contributing to the sides of the cranium Landmarks: 1. Squamous sutures- point of articulation of the temporal bone with the parietal bone 2. External acoustic canal- canal leading to the eardrum and the middle ear 3. Mandibular fossa- the point where the mandible ( lower jaw) joins the cranium 4. Mastoid process- rough projection inferior and posterior to external acoustic meatus; attachment sites for muscles 5. Styloid process- attachment point for muscles and ligaments for the neck.

•The mastoid process, full of air cavities and so close to the middle air- a trouble spot for infections- often becomes infected too, a condition referred to as MASTOIDITIS. Because the mastoid area is separated from the brain by only thin layer of bone, an ear infection that has spread to the mastoid process can inflame the brain coverings or meninges .The condition called MENINGITIS

The OCCIPITAL BONE most posterior bone of the cranium- forms floor and back wall. Joins the sphenoid bone anteriorly via its occipital regionLandmarks: 1. Lambdoid sutures- site of articulation of the occipital bone and parietal bone 2. Foramen Magnum- large opening in the base of the occipital, which allows the spinal cord to join with the brain. 3. Occipital condyles- round projection lateral to the foramen magnum that articulates with the first cervical vertebrae ( atlas)

The Sphenoid Bone Bat-shaped bone forming the anterior plateau of the middle cranial fossa across the width of the skull. The sphenoid bone is the keystone of the cranium because it articulates with all the cranial bones. Landmark:

1. Sella Turnica- central depression, a saddle-shaped region in the sphenoid midline. It encloses the pituitary gland.

The ETHMOID BONE

Irregularly shaped bone anterior to the sphenoid bone. Forms roof of the nasal cavity, upper nasal septum, and part of the medial orbit walls Landmarks:

1. Crista Galli ( cock’s comb) – vertical projection providing a point of attachment for the dura mater ,helping to secure the brain within the skull

2. Cribriform plates- bent plates lateral to the crista galli through which olfactory fibers pass to the brain from the nasal mucosa.

3. Superior and middle nasal conchae ( turbinates)- the conchae make air flow through the nasal cavity more efficient and greatly increase the surface area of the mucosa that covers them, thus increasing the mucosa’s ability to warm and humidify incoming air.

The Facial Bones 14 bones composing the face, 12paired, only the mandible and vomer are single bones. Hyoid bone, an additional bone, although not a facial bone but it is considered because of its location.

The MANDIBLE the lower jawbone, which articulates with the temporal bones in the only freely movable joints of the skull Landmarks:

1. Mandibular body- horizontal portion, forms the chin

2. Mandibular Ramus- vertical extensionof the body on either side

3. Coronoid Process- jutting anterior portion of the ramus; site of muscle attachment

The Maxillae or Maxillary Bone

two bones fused in the median suture; form the upper jawbone and part of the orbits . All facial bones, except the mandible,join the maxillae, thus they are the main or keystone bones of the face. Landmark:

1. Alveolar Margin- the inferior margin containing sockets in which the teeth lie.

The LACRIMAL BONE

fingernail sized bones forming a part of the medial orbit walls because the maxilla and the ethmoid. Each lacrimal boneis pierced by an opening ,the LACRIMAL FOSSA, which serves as a passageway for tears. Lacrimal is from the word Lacrimae ( means tears) , hence it is sometimes called tears bone.

The PALATINE BONE

paired bones posterior to the palatine process; form posterior hard palate and part of the orbit; meet medially at the median palatine sutures.

The ZYGOMATIC BONE

Lateral to the maxilla; forms portion of the face commonly called the cheekbone, and forms part of the lateral orbit.

The NASAL BONE

small rectangular bones forming the bridge of the nose

The VOMER blade – shaped bone( vomer= plow) in the median plane of nasal cavity that forms posterior and inferior nasal septum

The INFERIOR NASAL CONCHAE ( Turbinates) thin curved bones protruding medially from the lateral walls of the nasal cavity; serve the same purpose as the turbinate portions of the ethmoid bone.

The PARANASAL SINUSES•Four skull bones- maxillary, sphenoid, ethmoid and frontal- contains sinuses ( mucosa-lined air cavities) that lead to the nasal passages . These paranasal sinuses lighten the facial bones and may act as resonance chambers for speech. The maxillary sinus is the largest of the sinuses found in the skull. •Sinusitis or inflammation of the sinuses, occurs as a result of an allergy or bacterial invasion of the sinus cavities. The HYOID BONE located in the throat above the larynx. It serves as a point of attachment for the many tongue and neck muscles. It does not articulate with any other bone and is thus unique. It is a horseshoe-shaped with a body and two pairs of horns or cornua.

The Vertebral Column•Extending from the skull to the pelvis , forms the body’s major axial support.• surrounds and protects the delicate spinal cord via openings between adjacent vertebrae•Consists of 24 single bones called vertebrae and two composite or fused bones sacrum and the coccyx ,that are connected in such a way as to provide a flexible curved structure.•7 bones of the neck are called cervical vertebrae •Next 12 bones are called thoracic vertebrae •5 supporting the lower back are called lumbar vertebrae•Intervertebral discs , a pads of fibrocartilage that separates the vertebrae, cushion the vertebrae and absorb shock.

•The CERVICAL VERTEBRAE•Referred to as C1 through C2, forms the neck portion of the vertebral column.• C1 or also known as atlas ,receives the occipital condyles of the skull. The joint enables you to nod “yes”.•C2 or also known as axis, acts as pivot point for the rotation of the atlas (and the skull) above.•DENS or ODONTOID PROCESS- serves as the pivot point bet. atlas and the skull•The articulation between C1 and C2 allows you to rotate your head from side to side to indicate “ no”.•Vertebra prominens , spinous process of C7 ,that is visible through the skin, used as a landmark for counting the vertebrae.

The THORACIC VERTEBRAE•12 thoracic vertebrae ( referred to as T1 through T12) •Several characteristics of the thoracic vertebrae: larger body than the cervical vertebrae; it is somewhat heart-shaped, with two small articulating surfaces or costal facets facets articulate with the heads of the corresponding ribs oval or round shaped vertebral foramen long spinous process , with sharp downward hook the closer the thoracic vertebra is to the lumbar region, the less sharp and shorter the spinous process only vertebrae that articulates with the ribs

The Lumbar vertebrae•Five lumbar vertebrae ( L1 through L5) •Several characteristics of lumbar vertebrae: have massive blocklike bodies and short, thick, hatchet-shaped spinous processes extending directly backwards the sturdiest of the vertebraeSpinal cord ends at the superior edge of L2, but the outer covering of the cord, filled with the cerebrospinal fluid ,extends beyondLumbar puncture ( examination of the cerebrospinal fluid) or the administration of the “saddle block “ anesthesia for childbirth is normally done bet. L3 or L4 and L5, where ther is no chanceof injuring the spinal cord.

THE SACRUM• is a composite bone formed from the fusion of vertebrae • it articulates with L5 and inferiorly connects with the coccyx •Median sacral crest, is a remnant of the spinous process of the fused vertebrae•Alae or ala, formed by fusion of the transverse processes , articulate laterally with the hipbones•Sacral Foramina, are located at either end of the ridges , it allows blood vessels and nerves to pass

THE COCCYX • is formed from the fusion of three to five small irregularly shaped vertebrae, it is literally the human tailbone, a vestige of the tail that other vertebrates have•It is attached to the sacrum by ligaments

The THORACIC CAGE•Also known as the bony thorax, composed of the sternum, ribs and thoracic vertebrae.•Combined with the coastal cartilages it is called thoracic cage , because of its appearance and because it forms a protective cone-shaped enclosure around the organs of the thoracic cavity.

The STERNUM•Also known as breastbone ,a typical flat bone, is a result of the fusion of the three bones , manubrium, body, xiphoid process•It is attached to the first seven ribs. •Supriormost manubrium ,looks like a knot of a tie ; it articulates with the clavicle ( collar bone) laterally•Body also known as gladiolus, forms the bulk of the sternum• Xiphoid Process constructs the inferior end of the sternum and lies at the level of the fifth intercostal space. •It is made up of hyaline cartilage for children and ossified in adults

Bony landmarks of the sternum:

•Jugular notch , concave upper border of the manubrium, can be palpated easily, it is generally at the level of the third thoracic vertebra •Sternal angle ,is the result of the manubrium and body meeting at a slight angle to each other , reference point for counting ribs to locate the second intercostal space for listening to certain heart valves and for thoracic surgery •Xiphisternal Joint , point where the sternal body and xiphoid process fuse, lies at the level of the ninth thoracic vertebra

The RIBS• 12 pairs of ribs forms the walls of the thoracic cage• all of the ribs articulate posteriorly with the vertebral column via their heads and tubercles •First seven pairs are called true ribs or vertebrosternal , attached directly to the sternum by their own costal cartilages•Next five pairs are called false ribs ; they are attached indirectly to the sternum or entirely lack a sterna attachment.•Rib pair 8 to 10 are also called vertebrochondral , have indirect cartilage attachments to the sternum via the costal cartilage of the rib 7.•Floating ribs , last two pairs, have no sterna attachment.